Stream browning as a driver of benthic community change and degradation of the periphytic nutritional base
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
OP-Pohjola auditorium (L6)
Topic of the dissertation
Stream browning as a driver of benthic community change and degradation of the periphytic nutritional base
Doctoral candidate
Honours Bachelor Degree in Plant Science Joanna Brüsecke
Faculty and unit
University of Oulu Graduate School, Faculty of Science, Ecology and genetics
Subject of study
Stream Ecology
Opponent
Associate Professor André Frainer, The Arctic University of Norway (UiT)
Custos
Docent Jussi Jyväsjärvi, Centre for Economic Development, Transport and the Environment
Stream browning causes significant biodiversity change and a decline in the quality of a key resource
The world’s freshwaters are particularly vulnerable to human-induced changes, while also harbouring a significant fraction of the world’s biodiversity. This work homed in on the effects of one particular stressor to boreal streams. Freshwater browning is an ongoing process in boreal waters where inputs of land-derived organic matter, mainly in the form of dissolved organic carbon (DOC), cause the water colour to turn darker. In Finland, the main driver of this is the drainage of peatlands for forestry purposes.
The aim of this thesis was to investigate the effects of increased DOC concentrations on the communities living within forest streams affected by drainage and browning. Forest streams host a diverse range of communities, including microbes, macroinvertebrates and fish. This work focused on the microbial and macroinvertebrate inhabitants of small streams, to see how they respond to browning. The project was comprised of three parts.
First, the fatty acid composition of stream biofilm was analysed both from natural streams and an experimental setup. Second, macroinvertebrate samples were collected from the streams and analysed. And finally, the bacterial community was analysed using DNA and RNA from biofilm samples from the streams.
The fatty acid composition of the stream biofilm changed with browning in both the experimental setup and the natural streams. Omega-3 fatty acids (an important high-quality resource for consumers) declined, while the proportion of long-chain saturated fatty acids (a poor resource for consumers) increased.
We found a gradual decline in macroinvertebrate species richness and an abrupt shift in species composition at around 12-13 mg DOC L-1. Species known to be able to cope well with stressors increased, while many species declined. Algal scrapers, who feed by scraping biofilm containing algae off the rocks, were particularly affected.
The bacterial community also underwent major changes with browning. There were two shifts in community composition, one at low concentrations of 4-7 mg DOC L-1 and one at very high concentrations of 20 mg DOC L-1 and higher. There was also increased phylogenetic clustering in browner streams, which means the species in the community were genetically more similar to each other than would be expected by chance.
These findings are important for informing conservation efforts and the management of freshwaters.
The aim of this thesis was to investigate the effects of increased DOC concentrations on the communities living within forest streams affected by drainage and browning. Forest streams host a diverse range of communities, including microbes, macroinvertebrates and fish. This work focused on the microbial and macroinvertebrate inhabitants of small streams, to see how they respond to browning. The project was comprised of three parts.
First, the fatty acid composition of stream biofilm was analysed both from natural streams and an experimental setup. Second, macroinvertebrate samples were collected from the streams and analysed. And finally, the bacterial community was analysed using DNA and RNA from biofilm samples from the streams.
The fatty acid composition of the stream biofilm changed with browning in both the experimental setup and the natural streams. Omega-3 fatty acids (an important high-quality resource for consumers) declined, while the proportion of long-chain saturated fatty acids (a poor resource for consumers) increased.
We found a gradual decline in macroinvertebrate species richness and an abrupt shift in species composition at around 12-13 mg DOC L-1. Species known to be able to cope well with stressors increased, while many species declined. Algal scrapers, who feed by scraping biofilm containing algae off the rocks, were particularly affected.
The bacterial community also underwent major changes with browning. There were two shifts in community composition, one at low concentrations of 4-7 mg DOC L-1 and one at very high concentrations of 20 mg DOC L-1 and higher. There was also increased phylogenetic clustering in browner streams, which means the species in the community were genetically more similar to each other than would be expected by chance.
These findings are important for informing conservation efforts and the management of freshwaters.
Last updated: 29.8.2024